Device for adjustment of the anti-scattering grid to the focal length for radiological equipment

ABSTRACT

A device for the adjustment of the anti-scattering grid (G) of a radiological equipment to the different focal lengths that said equipment can provide includes a pair of pressing members (P) mobile in the direction transverse with respect to the plane of the grid (G), which is arranged and restrained between said pressing members (P) and a pair of corresponding underlying contrast members (C), the convex/concave profile of each pair of members (P, C) being obtained as locus of the local deformations, calculated point by point with a suitable spatial resolution, necessary to adjust the orientation of the segments of the grid (G) when going from one reference focal length to a second focal length.

This patent application claims the benefit of priority from ItalianPatent Application No. MI2002A 001763 filed Aug. 2, 2002 through PCTApplication Ser. No. PCT/IT03/00385 filed Jun. 23, 2003, the contents ofeach of which are incorporated herein by reference.

The present invention relates to radiological equipments, and inparticular to a device for the adjustment of the anti-scattering grid tothe different focal lengths that a radiological equipment can provide.

It is known that in radiological examinations involving significantamounts of matter there is generated a diffuse radiation whichnegatively affects the formation of the radiological image, since itgenerates an information not directly in correlation with theanatomic/morphologic structure of the part under examination.

Being not possible to eliminate the scattering since it is an intrinsiceffect of the interaction of X-rays with matter, there are usedanti-scattering grids which reduce the diffuse radiation which wouldreach the detector. Presently known grids are fixed focused grids, i.e.grids built with segments oriented along a certain angle specific for afocal length, which can be used only at the design length or at most fora limited range of focal lengths around the nominal focal length.Outside this range the grid is not usable in that it does no longerallow the transmission of the main radiation in a percentage useful forthe formation of the image.

For equipments with a wide range of the focus-detector distance, e.g.from 100 cm to 180 cm, the need arises to provide at least two grids andto allow the change of grid according to the type of examination, namelyto the focal length set on the equipment. The grid change implies adouble drawback both for the decrease in the intrinsic efficiency of theequipment and for the safety of the population, in terms of erroneousexposures.

In other words, the fact of having to change the grid when the focallength is modified dilates the times for carrying out the radiographiesand thus reduces the productivity of the equipment, besides involvingthe additional space taken up by the unused grid and possibledifficulties of change by inexperienced operators. Moreover, if theoperator does not change the grid this jeopardizes the result of theexamination, thus leading to a useless exposure of the patient who willhave to repeat the examination.

The first of these drawbacks is particularly limiting in the case of themodern equipments for digital radiology, characterized by a potentiallyhigh productivity thanks to the use as detector of a single digitaldetector (of the type with diodes and scintillator) suitable forexaminations both at short and long focal length and even without thepresence of the grid.

Therefore the object of the present invention is to provide a devicewhich overcomes the above-mentioned drawbacks.

This object is achieved by means of a device which bends the grid toadjust it when the focal length is modified. Other advantageous featuresare disclosed in the dependent claims.

The main advantage of the present device is exactly that of dispensingwith the grid change when the focal length is modified, so as tominimize the setup time of the equipment for a different examination andto optimize its exploitation.

In this way there is no space taken up by the second grid, the operatorhas no difficulties in changing the focal length and it is alwayspossible to have an optimal control of the scattering within the gridadjustment range.

In fact, rather than being satisfied with the fact that the distance iswithin the range in which the grid can be used, the latter isspecifically adjusted to the focal length set on the equipment. Forexample, a grid focused at 130 cm can usually be utilized for distancesbetween 110 and 150 cm, but thanks to the present device it can beprecisely adjusted for distances between 130 and 150 cm with the rangeof use extended up to 180 cm.

Another significant advantage stems from the fact that the gridadjustment can be easily made automatic and correlated with the settingof the focal length, whereby there is no longer the risk of the operatorforgetting it and the good outcome of the examination is sure.

These and other advantages and characteristics of the device accordingto the present invention will be clear to those skilled in the art fromthe following detailed description of an embodiment thereof, withreference to the annexed drawings wherein:

FIG. 1 is a diagram showing the principle of the adjustment of the gridupon modification of the focal length;

FIG. 2 is a top plan diagrammatic view of the present device;

FIG. 3 is a diagrammatic view in vertical section along line III—III ofFIG. 2, with the device in the rest position;

FIG. 4 is a view similar to the preceding one with the device activated;

FIG. 5 is a diagrammatic front view showing a possible driving systemfor the device;

FIG. 6 is a longitudinal vertical section along line VI—VI of FIG. 3 ofthe grid mounting system; and

FIG. 7 is a Cartesian chart with the data relating to a specificembodiment of the device.

Starting from the diagram of FIG. 1, there is first illustrated theprinciple on which the operation of the present grid adjustment deviceis based.

Indicating with f1 a first longer focal length and with f2 a secondshorter focal length, with p1, q1 and p2, q2 there are indicated theorientations required for said respective focal lengths to two segmentslocated respectively at x and x′ distance from the focal axis whichcoincides with the midplane of the grid, the latter being indicated bythe dotted reference line r.

To go from p1 to p2 the reference line r, i.e. the grid, should rotateto the position corresponding to the dotted line 1, whereas to go fromq1 to q2 it should rotate to the position of the dotted line 1′. Asclearly shown by said diagram, the grid should therefore rise at aheight d at distance x, which height d is much smaller than the heightresulting at line 1′ required to obtain a height d′ at distance x′.

This means that a rigid rotation of the grid is inadequate, as well as amere translation, and it is necessary that the grid takes a profiledefined as locus of the local deformations d, d′, etc. calculated pointby point with a suitable spatial resolution. A specific example of sucha calculation is illustrated further on, while now the general structureof the device and its simple yet effective operation will beillustrated.

With reference to FIGS. 2 to 6, there is seen that a device according tothe present invention essentially consists of a pair of contouredpressing members P mobile in the direction transverse with respect tothe plane of the grid G, which is arranged between these elements P andcorresponding underlying contrast members C.

More specifically, grid G is inserted in guides formed on the inside atthe top of the contrast members C and is also centrally secured topressing members P through plates L screwed thereon from below, asbetter illustrated in the detail of FIG. 6. To make up for the thicknessof plates L, in members C there are formed corresponding recesses Ksuitable to receive plates L (FIG. 4).

Between the pressing P and contact C members there are return springs Uwhose resistance must be overcome to operate the device, and which arethen used to return it to its rest position. FIG. 5 illustrates adriving system by means of a cable F passing over pulleys E, E′respectively arranged on members P, C so that by pulling on cable F saidelements are brought near and by releasing it springs U return them tothe rest position. Obviously the pull on the cables, one for each pairof members P and C, will be exerted by means of a motorized drumprovided with an end stop both in the opening and closing direction andcontrolled in correspondence with the setting of the focal length.

It should be noted that the scheme of FIG. 5 is merely indicative of thetype of drive, in that actually the push on the pressing members P doesnot take place directly through pulleys E, E′ but rather through members(not shown) carrying said pulleys B and vertically sliding on a fixedstructure on which pulleys E′ are mounted. This in necessary to allowthe removal of grid G in the case of examinations which do not requireit, whereby the group of grid G, pressing members P and contrast membersC (connected through crossbars X, see FIG. 6) forms a rcmovable frame.

This possibility of removal of grid G is diagrammatically illustrated inFIG. 2, which shows retaining clips R carrying blocking teeth B formounting said frame on said fixed structure. The presence of the grid isalso detected by a suitable sensor S, while its position in abutment onteeth B is guaranteed by biasing springs M which also make easier itsremoval when clips R are widened to disengage the removable frame.

In the table hereunder there is now illustrated an example of a specificcalculation of the deformations at a plurality of points along the grid,where with alpha1 and alpha2 there are indicated the angles (in radians)which the segments must have respectively for a focal length f1 of 150cm and for a length f2 of 130 cm, and with δ their difference from whichthe required local deformation is obtained. It should be noted thatalthough the table includes the calculations only at a few points, theactual resolution of calculation is in the order of 5 mm whereby theprofile of members P, C is obtained with such a resolution and thenjoining the points thus calculated.

In the chart of FIG. 7 there is shown the deformation line obtained byconnecting these calculated points and which can be approximated by aparabolic curve having the equation:y=−0.0001x ²−0.0006x+0.0082

Clearly with a curve of higher order it would be possible to achieve aneven better approximation, but as previously explained such a curve hasa merely indicative purpose since the actual embodiment of the deviceprovides the use of the real values point by point.

It is clear that the above-described and illustrated embodiment of thedevice according to the invention is just an example susceptible ofvarious modifications. In particular, the device driving system may beof any kind, e.g. with hydraulic, pneumatic or electric actuators,possibly dispensing with springs U, and similarly the systems forretaining grid G between members P, C and the whole removable framewithin the fixed structure may be somewhat changed by using othermechanically equivalent components.

Furthermore it should be noted that the device could also be reversed ifit is desired that the grid is undeformed at the shorter focal lengthand deformed at the longer one. In other words, in this case thepressing member P would be concave and would carry grid G whereas thecontrast member C would be convex and centrally connected to the gridthrough a plate, i.e. the device would in practice be rotated through180° around a horizontal axis.

Finally, it is obvious that the specific values indicated forexemplificative purpose are non-limiting in that the deformation profilewill change according to the reference focal length adopted and to theamount of the difference between the two focal lengths.

1. Device for an adjustment of an anti-scattering grid (G) of a radiological equipment to different focal lengths (f1 f2) that said equipment can provide, characterized in that it includes a first pressing member (P) located at a first end of the device and a second identical pressing member (P) located at an opposite end of the device, both said pressing members (P) being mobile in the direction transverse with respect to the plane of the grid (G), which is arranged and restrained between said pressing members (P) and a pair of identical corresponding underlying contrast members (C) located respectively under said first and second pressing members (P), and in that each pair of pressing members (P) and contrast members (C) has a convex/concave profile corresponding to the locus of the local deformations (d, d′, . . . ), calculated point by point with a suitable spatial resolution, necessary to adjust the orientation of the segments of the grid (G) when adjusting the grid (G) to go from a first focal length (f1) taken as a reference to a second focal length (f2).
 2. Device according to claim 1, characterized in that the reference focal length (f1) is longer than the second focal length (f2) and the pressing (P) and contrast (C) members respectively have a convex profile and a concave profile.
 3. Device according to claim 1 or 2, characterized in that the concave profile member is adapted to secure the grid (G) by introducing the grid (C) into lateral end guides, and in that the convex profile member is adapted to secure the grid (G) by means of a central plate (L) which enters a corresponding recess (K) formed on said concave member.
 4. Device according to claim 3, characterized in that return springs (U) are arranged between the pressing member (P) and the contrast member (C).
 5. Device according to claim 3, characterized in that the driving of the device is achieved by means of cables (F), one for each pair of members (P, C), passing over pulleys (E, E′) suitable to transmit a pressing action to the pressing members (P), the pull on said cables (F) being exerted by a motorized drum provided with end stops both in the device closing and opening direction.
 6. Device according to claim 3, characterized in that the contrast members (C) are connected by crossbars; and the grid (G), the pressing members (P) and the contrast members (C) connected by said crossbars form a removable frame introduced into a fixed structure and blocked therein by a retention system.
 7. Device according to claim 6, characterized in that the retention system of the removable frame consists of retaining clips (R) carrying blocking teeth (B), the position of the frame in abutment on said teeth (B) being guaranteed by biasing springs (M) also suitable to make easier the removal of the frame when said clips (R) are widened to disengage it.
 8. Device according to claim 1 or 2, characterized in that return springs (U) are arranged between the pressing member (P) and the contrast member (C).
 9. Device according to claim 8, characterized in that the driving of the device is achieved by means of cables (F), one for each pair of members (P, C), passing over pulleys (E, E′) suitable to transmit a pressing action to the pressing members (P), the pull on said cables (F) being exerted by a motorized drum provided with end stops both in the device closing and opening direction.
 10. Device according to claim 8, characterized in that the contrast members (C) are connected by crossbars and of the grid (C), the pressing members (P) and the contrast members (C) connected by said crossbars form a removable frame introduced into a fixed structure and blocked therein by a retention system.
 11. Device according to claim 10, characterized in that the retention system of the removable frame consists of retaining clips (R) carrying blocking teeth (B), the position of the frame in abutment on said teeth (B) being guaranteed by biasing splings (M) also suitable to make easier the removal of the frame when said clips (R) are widened to disengage it.
 12. Device according to claim 1 or 2, characterized in that the driving of the device is achieved by means of cables (F), one for each pair of members (P, C), passing over pulleys (E, E′) suitable to transmit a pressing action to the pressing members (P), the pull on said cables (F) being exerted by a motorized drum provided with end stops both in the device closing and opening direction.
 13. Device according to claim 5, characterized in that the contrast members (C) are connected by crossbars and the grid (G), the pressing members (P) and the contrast members (C) connected by said crossbars form a removable frame introduced into a fixed structure and blocked therein by a retention system.
 14. Device according to claim 13, characterized in that the retention system of the removable frame consists of retaining clips (R) carrying blocking teeth (B), the position of the frame in abutment on said teeth (B) being guaranteed by biasing springs (M) also suitable to make easier the removal of the frame when said clips (R) are widened to disengage it.
 15. Device according to claim 1 or 2, characterized in that the contrast members (C) are connected by crossbars (X); and of the grid (G), the pressing members (P) and the contrast members (C) connected by said crossbars (X) form a removable frame introduced into a fixed structure and blocked therein by a retention system.
 16. Device according to claim 15, characterized in that the retention system of the removable frame consists of retaining clips (R) carrying blocking teeth (B), the position of the frame in abutment on said teeth (B) being guaranteed by biasing springs (M) also suitable to make easier the removal of the frame when said clips (R) are widened to disengage it.
 17. Device according to claim 16, characterized in that it further includes a sensor (S) suitable to detect the presence of the grid (G).
 18. Device according to claim 15, characterized in that it further includes a sensor (S) suitable to detect the presence of the grid (G).
 19. Radiological equipment providing different focal lengths (f1, f2), characterized in that it includes a device for an adjustment of the anti-scattering grid (G) according to claim
 1. 